Fastener installation presses typically are comprised of an escapement means to deliver a fastener to a designated position under a press ram, plus the mechanism of the ram itself which delivers the fastener, usually with some amount of high force, to a workpiece, whereupon the fastener is pressed firmly into the workpiece.
It is of the utmost importance to provide point-of-operation safety that detects an unsafe condition in the working of such presses. Heretofore, the method of providing such safety for both worker and workpiece has been accomplished in some presses by using a sensing means on or about the ram itself to provide absolute position sensing of the ram, plus switch means integral with a sliding, spring-loaded sleeve (punch adapter) at the end of the ram.
Machine electronics compare the location of the ram with the status of the switch to determine if an unsafe condition exists. Displacement of the punch assembly at any point outside of the working zone of operation halts the ram. Such unsafe conditions which would cause the punch adapter to move include contacting a worker's hand or finger in the path of the descending ram, a misplaced workpiece, or a misaligned fastener.
Other types of sensing may also be used, such as normally developing an electrical contact between the punch and the workpiece, wherein the lack of such contact serves to detect a worker's finger. Presses employing one or a combination of the above sensing means are used in press models HP2.5, HP6, and HP10 manufactured by Haeger, Inc., Oakdale, Calif.; press model AS-7.5 manufactured by Auto-Sert, Inc., Minneapolis, Minn.; or PEMSERTER Series 2000 presses manufactured by Penn Engineering & Manufacturing Corp., Danboro, Pa.
Typical in the industry and employed by all of the aforementioned presses, the ram sensing means is connected to the press electronics by a cable. As the ram strokes up and down through several thousands of cycles installing fasteners, this cable is subject to chaffing, wear, and breakage, leading to replacement, downtime, warranty costs, etc. The safety means is usually inherently safe, in that a broken cable and thus a missing signal, is detected as a fault, and the machine electronics signal a valve to halt the descending ram. However, should the cable break in such a manner that the conducting wires of the cable come in contact with each other, no fault would be detected and worker safety could be compromised. Furthermore, the workpiece which might be damaged could be a very costly assembly, such as a multilayered printed circuit board that might have to be scrapped. At the very least, the press is subjected to downtime, and production delays are experienced during the replacement of the damaged cable.
There is therefore a need to eliminate the cable that connects the end of ram sensing means to the press frame, while still being able to detect the movement of the punch adapter, and thus a possible unsafe condition.